strengthening Weak plywood floor

i hope i can explain this well. In my kitchen that i want to tile, i have a small roughly 7'x7' area that is an old addition. (nothing in this house was ever done right). The floor joist are 2x6 but are 3 wide on each one. the joist are vey solid, the problem is the 1/2" plywood on top gives under foot between the joist. Is adding another 2x6 between the other joist the only option? i have about 11.5" between joist now, adding another would cut space down to about 5" between. Will adding 11.5" plywood 3/4"thick to the underside of the sub floor do anything? I know adding to the the top would be better but it throws off doorways, cupboards, and other flooring in same room. i hope you understand what i am saying.

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strengthening Weak plywood floor

Jpaz,
How about this? The green represents the new wood. Screw 3/4 plywood between the existing joists, and then add 3/4 to the sides of the joists to support the additional 3/4 plywood flooring. Using 3/4 on the joist would provide downward support and add less overall weight. That's my first thought.

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Last edited by RetiredSoldier; 10-13-2011 at 08:09 PM.

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strengthening Weak plywood floor

Are you speaking of ceramic tile or vinyl tile?
For ceramic tile the floor needs to be rigid, very rigid.
The 2x6's might be an issue depending on how far they span.
The subfloor of 1/2" ply is way too thin. You would need to add at least another 5/8" on an adequate joist system to put down ceramic tile.

strengthening Weak plywood floor

retiredsoldier, i like that idea. wish i would've thought of it! have you ever used this setup? thank you for the illustration its great. ron6519, i am useing porcelain tile. with each joist being 3 2x6's nailed together and the span being only 7' the joist themselves are very sturdy. its just the fact they didnt let enough hight for the correct size sub floor so the 1/2" plywood gives alittle between joist when you step on it.

strengthening Weak plywood floor

Quote:

Originally Posted by jpaz

retiredsoldier, i like that idea. wish i would've thought of it! have you ever used this setup? thank you for the illustration its great. ron6519, i am useing porcelain tile. with each joist being 3 2x6's nailed together and the span being only 7' the joist themselves are very sturdy. its just the fact they didnt let enough hight for the correct size sub floor so the 1/2" plywood gives alittle between joist when you step on it.

I used this in my 5x9 bathroom. I originally wanted to install tile, but decided to use this http://www.homedepot.com/Flooring-Vi...atalogId=10053 after seeing them at the home improvement store. They look just like real tile and will flex a little with the floor if you can't get it absolutely free of bounce. I grouted them and people think they are tile. It's been over a year, and no problems. If you go with real tile, I recommend using Ditra or some simular type of underlayment to provide the separation that will limit possible cracking of your tile.

strengthening Weak plywood floor

if i were doing the work i would beef up the floor by installing 3/4" plywood over top of the existing floor if not an additional layer of 1/4", both gluing and screwing it down using construction adhesive

the only reasoning i can see retired soliders technique helping is to give additional hold for the screws going through the new plywood. it wont provide very much strength as you will be instlaling it in several peices.. multiple joints = a weaker floor. this is the whole reason behind using sheet goods. they provide far superior strength as compared to t&g boards

strengthening Weak plywood floor

If you beef up the joists as RetiredSoldier described AND screw & glue, you won't have any issues, IMHO.

Yes, you are using pieces but with the proper adhesive and screwing, the 3/4 and 1/2 will in effect become 1 1/4 flooring. Just make an effort in keeping everything as flush as possible and be generous with the glue and scews. Your strength will be there. It's just a matter of making sure there is no play, which screw/glue will take care of. You could consider using a flexible grout also.

Can you not put down 5/8 flooring instead of 1/2 as it's not that great of a difference and would be even better? You're going to have to accomodate for the tile anyhow....

strengthening Weak plywood floor

My unprofessional opinion is that you provide a 'platform' (say 6" X 6" or 6" diameter minimum) for the column to rest on to distribute the load over a wider area than just the 3" or 4" diameter column. Now what the platform might be made of and how it is constructed are other matters. 1/4" or 3/8" steel might work well. Set the steel plate on your slab with a high strength concrete 'bed' and you might have it. Just guessing.